At around 2am this morning, police were called to the Bury area of the M66, between junction one and two.
A grey Mercedes E220 was travelling along the northbound carriageway when it passed onto the slip road at junction two.
At this point, the car collided with a woman in lane one.
The woman – who is believed to be in her 40s – suffered fatal injuries and was sadly pronounced dead.
The carriageway was closed for around 10 hours but has since been re-opened.
Officers investigating the circumstances around the collision are appealing for witnesses and those with dashcam footage to come forward.
Police Sergeant Joe Barron of GMP’s Serious Collision Investigation Unit, said: “This incident caused a lot of disruption throughout the morning and into the day and I know the impact this had on motorists so I’d like to thank them for their patience as we’ve carried out our enquiries.
“I appreciate from what we know at the moment, this seems an unusual set of circumstances but our team will continue carrying out the enquiries we need to do until we find out exactly what happened.
“As it was early in the morning, there weren’t many people in the area at the time but if anyone witnessed what happened or has any CCTV, please contact us as a matter of urgency.
“My thoughts remain with the woman’s family and we will continue to support them through our investigation as they come to terms with this terrible news.”
Anyone with information should contact GMP’s Serious Collision Investigation Unit on 0161 856 4741 quoting reference number 147 of 02/05/19 or the independent charity Crimestoppers, anonymously, on 0800 555 111.